1. Technical Field
The present invention generally relates to Bragg gratings and, more particularly, to an apparatus and method for producing high quality fiber optic Bragg gratings with precise control of the Bragg center wavelength.
2. Discussion
Most fiber optic Bragg gratings are manufactured by exposing the core of a fiber to an intense, spatially modulated ultra violet (UV) beam of radiation. The UV light induces an increase in the index of refraction of the core material in the fiber optic. Thereafter, light launched down the core of the fiber is reflected only if the spatial modulation period (.LAMBDA.) and the wavelength of the light (.lambda.) satisfy the Bragg condition, .lambda..sub.B =2n.LAMBDA., where n is the mean index of refraction in the fiber core.
According to the prior art, precise positioning of the reflection wavelength center in fiber optic Bragg gratings requires tedious re-alignment of the optics. The production of holographic fringe patterns having appropriate fringe spacing requires precise positioning of the beam combining optics such as the prism and cylindrical lens in prism techniques and the beam splitter, combining mirrors and focusing lenses in open holographic techniques. This makes the production of fiber optic Bragg gratings time consuming and commercially impractical on a large scale basis. As such, there is a need in the art to provide an apparatus and method for routinely producing fiber optic Bragg gratings with precise control of the Bragg center wavelength.